The application of human reliability analysis to carpal tunnel decompression

Introduction Many surgical procedures are prone to human error, particularly in the learning phase of skills acquisition. Task standardisation has been suggested as an approach to reducing errors, but it fails to account for the human factors associated with learning. Human reliability analysis (HRA) is a structured approach to assess human error during surgery. This study used HRA methodologies to examine skills acquisition associated with carpal tunnel decompression. Methods The individual steps or subtasks required to complete a carpal tunnel decompression were identified using hierarchical task analysis (HTA). The systematic human error reduction and prediction approach (SHERPA) was carried out by consensus of subject matter experts. This identified the potential human errors at each subgoal, the level of risk associated with each task and how these potential errors could be prevented. Results Carpal tunnel decompression was broken down into 46 subtasks, of which 21 (45%) were medium risk and 25 (55%) were low risk. Of the 46 subtasks, 4 (9%) were assigned high probability and 18 (39%) were assigned medium probability. High probability errors (>1/50 cases) included selecting incorrect tourniquet size, failure to infiltrate local anaesthetic in a proximal-to-distal direction and completion of the World Health Organization (WHO) surgical sign-out. Three (6%) of the subtasks were assigned high criticality, which included failure to aspirate before anaesthetic injection, whereas 21 (45%) were assigned medium criticality. Remedial strategies for each potential error were devised. Conclusions The use of HRA techniques provides surgeons with a platform to identify critical steps that are prone to error. This approach may improve surgical training and enhance patient safety.


Introduction
Carpal tunnel decompression, indicated for median nerve entrapment at the wrist, is one of the most common elective hand procedures, with approximately 1,700 being performed per year in Ireland with an incidence of 3.54 per 10,000. 1 Although complications rates are typically low (reported incidence range 0.07%-1.2%),][4] Carpal tunnel decompression is one of the first procedures a trainee surgeon will learn to perform independently given the numbers performed and the perceived low complexity.However, the early phase of learning may be prone to human error. 5Standardisation has been suggested as an approach to reducing error during learning but does not account for the impact of any individual step in the process. 6uman reliability analysis (HRA) is an approach that identifies systematically the impact of human error on a system to reduce adverse events and complications. 7First developed for use in aviation, HRA has been adopted widely by many industries, including the military and nuclear power generation. 8,91][12][13] This study is the first to apply HRA in hand surgery.
Hierarchal task analysis (HTA) and the systematic human error reduction and prediction approach (SHERPA) are two recognised techniques in HRA.HTA refers to the systematic decomposition of a procedure into its component steps with a specific focus on the human factors that contribute to a safe outcome. 10nalyses are dependent on multiple subjective observations and recording of variations in expert clinical practice to produce a single accepted optimum method for successful task completion. 10SHERPA is an error reduction and prediction approach.SHERPA identifies credible errors in a process and suggests methods of error mitigation at each step.HTA serves as a framework for the application of SHERPA to identify the errors.
Applying HRA techniques such as HTA and SHERPA to carpal tunnel decompression allows trainees to view the steps in a concise manner, showing sequential tasks required to complete the procedure, highlights steps prone to error and alerts the trainee to steps in which error criticality is high.
This study aims to develop an HTA for carpal tunnel decompression and to analyse identified errors using SHERPA methodology.The resultant framework serves as a useful tool for surgical trainers and trainees.

Methods
A standard approach for completing an HTA and SHERPA was adopted. 6This approach consisted of three stages: firstly, the identification of the procedure for analysis, followed by the HTA to identify key subtasks and finally the SHERPA analysis.Each of these three stages are outlined below.

Identification of procedures for analysis
Carpal tunnel decompression typically follows a wellrecognised sequence of surgical steps, taking into account anatomical variation.If an error occurs at a critical step, the consequences can lead to permanent disability for the patient.These factors mean that carpal tunnel decompression is eminently suitable for HTA.

Hierarchal task analysis
HTA enables the systematic distillation of a carpal tunnel decompression procedure into its component steps.These subtasks are chosen with a specific emphasis on the human errors that can occur.We produced an HTA that identified all errors that could likely occur and the mitigating avoidance steps needed to prevent them.

Literature review:
A detailed literature review was conducted to identify relevant literature relating to the appropriate technique and best practice for carpal tunnel decompression.An extensive search of PubMed, Medline, UpToDate and Scopus was performed to construct an initial HTA for carpal tunnel decompression. 14,15Notable findings include the risk of iatrogenic median nerve injury, reported in 0.55% cases. 16Up to 70% of iatrogenic median nerve injuries occur during carpal tunnel decompression. 17Postoperative surgical site infection is a rare but serious complication following open carpal tunnel decompression.9][20] The American Society for Surgery of the Hand (ASSH) estimate the incidence of wrong site surgery in hand surgery as 1 in 27,686 or 0.00003%. 21,22servation: A total of 20 observations of the carpal tunnel decompression procedure were performed in our institution between January and July 2022.Four consultant plastic surgeons (Tang and Giddins Grade III-IV), performed all cases. 23During each observation, the steps taken by the experts were recorded and used to modify the task list.

Subject matter experts:
Five consultant plastic surgeons were then recruited as subject matter experts (SMEs) for the development of the final HTA.The SMEs performed the initial review of the data gathered from the literature and procedure observations.This iterative process refined the HTA until a single, optimum method for the completion of the task was constructed.

Construction of HTA
The initial HTA was constructed by an experienced plastic surgery fellow and a consultant plastic surgeon.A standard approach was used to develop this, as described below.
• The overall goal is identified (e.g.completion of a carpal tunnel decompression) • The series of steps that are required to achieve this goal are identified; these are known as subtasks.It is a matter of judgement as to the level of detail assigned to individual subtasks.To illustrate, a subgoal could be "complete WHO Time Out Checklist", or it could be more detailed (i.e.confirm all team members have identified themselves by name and role, verbally confirm the patient, site and procedure, has antibiotic prophylaxis been given, has essential imaging been displayed, etc).The level of detail required was determined by consensus between the five SMEs carrying out the SHERPA based upon whether further decomposition was deemed to add little value.

Systematic human error reduction and prediction approach
Based on literature review and expert consensus, the probability of each error was assigned along with its criticality.Once the error was identified, an error mitigation strategy was suggested.The SHERPA analyses were carried out by the same five surgeons who constructed the HTAs (Tang and Giddins Grade III, IV). 23he five surgeons worked together to carry out the SHERPA analysis.Any disagreements were resolved through discussion until consensus was reached.The method used to complete the SHERPA analysis was as follows: • subtasks were classified based on the behaviour involved, from the following: o action (e.g.incise skin along full skin marking), o retrieval (e.g.complete WHO sign-out checklist), o checking (e.g.checking LA has provided adequate anaesthesia), o selection (e.g.choosing correct size tourniquet for patient), o information communication (e.g.complete WHO time-out checklist).
• Using the classification of error types (Table 1), errors were determined that could credibly occur during performance of the different subtasks.
For example, points occurring later in the HTA where the error could be identified before it had an effect were noted.
• The "criticality" of each error was rated using three levels: o low, unnoticeable clinical effect o medium, transient clinical effect o high, permanent clinical effect. 6,24The probability and criticality scores were multiplied together to calculate the level of risk.A score from 0 to 2 was considered "low risk", from 3 to 6 "medium-risk" and 7 to 12 "high-risk".
• Potential remedial strategies were suggested to prevent each error from occurring or propagating at the individual level, the equipment level, the environmental level and the organisational level.

Results
A total of 20 open carpal tunnel decompression procedures, performed by four consultant plastic surgeons, were observed for the purposes of the study.These observations were then used to further refine the HTA that had been constructed already through literature review and experience from two of the SMEs (Tang and Giddins Grade III-IV). 23A simplified carpal tunnel HTA is demonstrated in Table 2.The complete HTA, with all subtasks described, is also shown (Supplemental Material A); 13 principal tasks and 46 subtasks were identified.
Table 3 demonstrates the SHERPA analysis for carpal tunnel decompression.Of the errors identified at each subtask, the maximum risk score assigned was 6, which falls into the medium-risk category.A total of four subtasks had a risk score of 6, with a total of 18 subtasks meeting the criteria for the medium risk category.This highlights which errors have the potential for permanent clinical effect.High probability errors (>1/100 and <1/50 cases) included selecting incorrect tourniquet size, failure to sterilise the skin before administration of local anaesthetic (LA), failure to infiltrate LA in a proximal-to-distal direction and failure to complete the WHO surgical sign-out.
Three subtasks were identified as high criticality, i.e. having the potential to cause permanent clinical effect.These included failure to expel air from the syringe before LA administration, failure to aspirate the syringe before infiltrating the local anaesthesia and failure to complete the WHO time-out checklist before skin incision.Although more subtasks identified errors that were likely to occur, those subtasks were deemed unlikely to have a noticeable clinical effect.
Each error was then classified into a behaviour type: action, retrieval, checking, selection or information communication.Of the four errors deemed to have a high occurrence probability, two were classified as action behavioursone as a selection behaviour and one as a retrieval behaviour.The errors classified as action behaviours included failure to sterilise the skin before administration of LA and failure to infiltrate LA in a proximal-to-distal direction.The error classified as selection behaviour was selecting incorrect tourniquet size.Finally, the error with high probability of occurring that was classified as retrieval behaviour was failure to complete the World Health Organization (WHO) surgical sign-out.Errors classified as retrieval behaviours relate to information

Discussion
When acquiring new skills during training, young surgeons are naturally more prone to error.It has been suggested that standardisation, using HRA, is an approach to reducing error during surgery.This study examined a commonly performed procedure and highlighted several important steps in open carpal tunnel decompression that were felt to have the potential for serious adverse outcome.Our study also provided a framework that can be utilised in surgical education and simulation-based training with the potential to aid in skill acquisition and error-reduction.
As described in other HRA reports, this study was led by healthcare clinicians rather than healthcare safety experts.In some industries, this type of analysis is carried out by a dedicated safety expert, such as the nuclear power industry.In this setting, however, it is more beneficial that the analysis is carried out by those performing the procedure to increase the validity of the analysis. 6n optimum technique for each procedure is necessary for standardisation to be effective.Standardisation was achieved in the current study, through the iterative process of HTA.It is difficult to apply HRA to emergency procedures or complex, major cases where surgical variation can be high and patient factors can play a large role.While aiming to reduce error and simplify processes, applying HRA to emergency cases may add further burden to an already time-sensitive procedure.More complex cases with a large degree of variability, can be more difficult to analyse.The optimum technique to carry out a procedure is therefore more applicable to procedures such as carpal tunnel release.
We identified failure to aspirate syringe during local anaesthetic as an error of potential high criticality.The true incidence of air embolism following intravascular injection of local anaesthesia in peripheral nerve surgery is unknown.However, the potential side effects are well A limitation of this study, seen throughout HRA methodologies both in healthcare and other industries, is the limited number of SMEs from a single institution available to provide input on constructing the HTA and developing the SHERPA analysis. 6,7This study included input from five SMEs from a single institution.The HTA was derived from a combination of SME input and literature review.However, input from further SMEs from other surgical specialties who also perform open carpal tunnel decompression such as orthopaedic surgery, may have benefited the SHERPA analysis.
While this generic framework for carrying out open carpal tunnel decompression could be applied to a number of other commonly performed procedures and utilised in surgical education and simulation, it must be noted that there will inevitably be some variation in clinical practice both across surgical specialities and across different surgical units.If HTA is to be used in teaching surgical trainees operating in surgical units across the globe, variation in clinical practice should allow for experts across specialities and across units to refine the HTA according to their own variation in technique for performing the individual procedures.However, if HTA is to be effective in reducing error, it is important that internal agreement be reached at each unit to prevent large variations in practice being taught to surgical trainees.
HRA has substantial implications for improvement in both the training and assessment of trainee surgeons.A standardised protocol that assigns risk to subtasks can guide trainees to improve their operative skills and can address concerns in allowing trainees to perform technically challenging steps, while enhancing patient safety by reducing errors.
Open Access This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, reproduction, and adaptation in any medium, provided the original work is properly attributed.

Table 1
Error classification used in SHERPA Of the three errors that were deemed high criticality, two were classified as action behaviours and the third was classified as an information communication behaviour.The errors classified as action behaviours included failure to expel air from the syringe before LA administration, failure to aspirate the syringe before infiltrating the local anaesthesia.The error classified as an information communication behaviour was failure to complete the WHO time-out checklist before knife to skin.

Table 2
Simplified carpal tunnel decompression HTA

Table 3
SHERPA analysis for carpal tunnel decompression LA = local anaesthetic; SHERPA = systematic human error reduction and prediction approach; WHO = World Health Organization Ann R Coll Surg Engl 2024; 106: 432-438